FBI Director James Comey has told Congress he has not changed a conclusion reached in July that Democratic presidential candidate Hillary Clinton did nothing criminal in using a private server for emails when she was secretary of state.

Comey made the announcement in a letter Sunday after the bureau reviewed a new batch of emails discovered during a separate investigation involving former U.S. Congressman Anthony Weiner, the estranged husband of key Clinton aide Huma Abedin.

In his letter to Congress, Comey said investigators have been "working around the clock" processing and reviewing the emails written to and by Clinton when she was secretary of state. Based on their review, he said, "we have not changed our conclusions that we expressed in July with respect to Secretary Clinton."

Comey said in July that while Clinton may have been "extremely careless" in handling classified information, there was no criminal intent and that prosecutors would reach the same decision.

Markets surge

Global financial markets rose following the announcement. Dow Jones index futures surged by about 200 points ahead of Monday's opening, according to the Associated Press.

Clinton communications director Jennifer Palmieri told reporters Sunday the campaign is "glad that this matter is resolved. We are glad to see that he (Comey) has found, as we were confident he would, that he's confirmed the conclusions that he reached in July."

Republican presidential nominee Donald Trump said Clinton is protected by a "rigged system," telling a crowd of supporters in Michigan that it is impossible to review "650,000 new emails in just eight days."